This chapter is from the book

Answers and Explanations

Objective 3.1

c. If two devices are connected to the same IRQ line, a conflict
occurs because it is not likely that the interrupt handler software can service
both devices. The IRQ3 line works for both COM2 and COM4. When an external modem
uses the COM2 port, no other device should use the COM4 port.

c. In the case of a complete shutdown, or a significant sag, the
best protection from losing programs and data is an uninterruptible power supply
(UPS). A UPS is a battery-based system that monitors the incoming power and
kicks in when unacceptable variations occur in the power source.

b. The primary mission of the UPS is to keep the system running
when a power failure occurs. Because it's battery based, it cannot keep the
system running infinitely. For this reason, you should not connect nonessential,
power-hungry peripheral devices such as a laser printer to the UPS
supply.

d. An uninterruptible power supply is an extremely good
power-conditioning system. Because it always sits between the commercial power
and the computer, it can supply a constant power supply to the system to protect
it from spike damage.

d. If a UPS is being used to keep a critical system in operation
during the power outage, the high current drain of the laser printer would
severely reduce the length of time that the UPS could keep the system
running.

d. Overvoltage conditions are classified as surges when their
duration is measured in milliseconds or longer.

a. Overvoltage conditions are classified as spikes when their
duration is measured in nanoseconds or less.

b. A surge suppressor protects the system from damages caused by
minor power line interruptions. It passively filters the incoming power signal
to smooth out variations.

a. A cooling fan should be placed on any IC operating at clock
speeds above 33MHz.

d. Uninterruptible power supplies are battery-based systems that
monitor the incoming power and kick in when unacceptable variations or outages
occur in the power source.

c. A surge suppressor is used to protect computer equipment from
very small overvoltage occurrences by passively filtering the incoming power
signal to smooth out variations.

b. Sags, an undervoltage condition, can include voltage sags and
brownouts. A voltage sag typically lasts only a few milliseconds, but a brownout
can last for a protracted period of time. Sags can cause the system to suddenly
reboot because it thinks the power has been turned off.

a. A brownout is an undervoltage condition and can last for a
protracted period of time, which makes it easy to spot.

c. If a monitor is to be left on for an extended period of time
with the same image on it, this can cause the image to become permanently
"burned" into the phosphorous coating. To prevent this from occurring,
install a screensaver package to constantly refresh the contents of the
display.

b. To recover from hardware failures, operator mistakes, and acts
of nature, you should make system backups of the hard drive.

a, b. (a) Copies of the system backup should be stored in a
convenient but secure place. In the case of secure system backups, such as
client/server networks, the backup copies should be stored where the network
administrators can have access to them, but not the general public (for example,
a locked file cabinet). (b) Many companies maintain a copy of their
backup away from the main site. This is done for protection in case of disasters
such as fire.

c. If your trackball mouse responds erratically when you move it
across the screen, the first thing you should do is clean the mouse. Use a
lint-free swab to clean the X and Y trackball rollers inside the mouse.

d. Because the CD-ROM stores data in the form of spots burned into
an optical media, the RFI escaping from the monitor would not affect it.
However, all of the other storage devices rely on magnetic storage that is
susceptible to damage from RFI and other magnetic-field disturbances.

c. The oxidation buildup occurring on electrical connectors and
contacts reduces the flow of electricity through the connection. Even with
proper handling, some corrosion can occur over time. This oxidation can be
sanded off with emery cloth, rubbed off with a common pencil eraser or special
solvent wipe, or dissolved with an electrical contact cleaner spray. The only
acceptable answer offered in this question is the use of contact
cleaner.

d. High humidity can lead to heat-related problems and
failures.

a. The application of an antistatic spray or antistatic solution
prevents the buildup of static charges on the components of the system. A
solution composed of 10 parts water and 1 part common household fabric softener
makes an effective and economical antistatic solution.

d. A damp cloth is the best general-purpose cleaning tool for use
with com-puter equipment, such as a monitor.

b. With a trackball mouse, the trackball should be removed and
cleaned periodically. Use a lint-free swab to clean the X and Y trackball
rollers inside the mouse.

d. Unlike the floppy disk drive, the mouse, and the printer, the
keyboard's electronic circuitry is open to the atmosphere and should be
vacuumed regularly. Dust buildup on the keyboard circuitry can cause its ICs to
fail due to overheating.

d. Manual cleaning of read/write (R/W) heads should be performed
with isopropyl alcohol using a foam swab. Cotton swabs can shed fibers that can
contaminate the drive and damage portions of its R/W head.

a, b, d. Sources of heat buildup around the computer and its
peripherals include direct sunlight from an outside window, locations of
portable heaters in the winter, and papers and books piled up around the
equipment.

b. Copies of the system backup should be stored in a convenient
but secure place. In the case of secure system backups, such as client/server
networks, the backup copies should be stored where the network administrators
can have access to them, but not the general public (for example, a locked file
cabinet).

d. High humidity can lead to heat-related problems.

a. Microcomputers are designed to run at normal room temperatures.
If the ambient temperature rises above about 85°F, heat buildup can become
a problem.

c. A static-free vacuum can be used to remove dust from inside
cases and keyboards. Be sure to use a static-free vacuum because normal vacuums
are, by their nature, static generators. The static-free vacuum has special
grounding to remove the static buildup it generates.

a, b. (a) The missing cover permits dust to accumulate in
the system, forming the insulating blanket that traps heat next to active
devices and can cause component overheating. (b) The missing slot cover
interrupts the designed airflow patterns inside the case, causing components to
overheat due to missing or inadequate airflow.

b. As with any electronic device, computers are susceptible to
failures caused by dust buildup, rough handling, and extremes in
temperature.

d. Oxidation can be removed from adapter card contacts with emery
cloth, rubbed off with a common pencil eraser or special solvent wipe, or
dissolved with an electrical-contact cleaner spray.

d. To remove dust from the inside of computer cases, a small
paintbrush is handy.

a. The outer-surface cleaning should be followed by the
application of an antistatic spray or antistatic solution to prevent the buildup
of static charges on the components of the system.

b. Outer-surface cleaning can be accomplished with a simple
soap-and-water solution, followed by a clear water rinse. Care should be taken
to make sure that none of the liquid splashes, or drips, into the inner parts of
the system.

a. Outer-surface cleaning can be accomplished with a simple
soap-and-water solution, followed by a clear water rinse. Care should be taken
to make sure that none of the liquid splashes, or drips, into the inner parts of
the system. A damp cloth is easily the best general-purpose cleaning tool for
use with computer equipment.

Objective 3.2

a. Normal operating vibrations and temperature cycling can degrade
the electrical connections between ICs and sockets over time. This gradual
deterioration of electrical contact between chips and sockets is referred to as
chip creep.

c. A Class C fire extinguisher specified for use around electrical
equipment should be on hand around computers.

b. The surge suppressor's clamping speed rating describes how
quickly it can react to changes in the incoming power level and act to minimize
it.

b. Proper grounding is the best defense against the disruptive
effects of EMI.

c. ESD is most likely to occur during periods of low humidity. If
the relative humidity is below 50%, static charges can accumulate easily. ESD
generally does not occur when the humidity is above 50%.

b. To avoid damaging static-sensitive computer devices, ground
yourself by touching the power supply housing with your finger before touching
any components inside the system. This technique will only work safely if the
power cord is attached to a grounded power outlet. The ground plug on a standard
power cable is the best tool for overcoming ESD problems.

c. Antistatic straps should never be worn while working on
higher-voltage components, such as monitors and power supply units.

a. Unlike ESD, which is the most damaging form of electrical
interference associated with digital equipment and is destructive, the effects
of EMI can be corrected without damage.

c. Professional service technicians use grounding straps to
minimize the chances of ESD during normal computer maintenance work involving
MOS devices. These antistatic devices can be placed around the wrists or ankles
to ground the technician to the system being worked on. These straps release any
static present on the technician's body, and pass it harmlessly to ground
potential.

b. Normal operating vibrations and temperature cycling can degrade
the electrical connections between ICs and sockets over time. This gradual
deterioration of electrical contact between chips and sockets is referred to as
chip creep. It is a good practice to reseat any socket-mounted devices when
handling a printed circuit board.

d. Of the possible choices provided, installing antistatic carpet
is the only option that will help to minimize ESD.

c. ESD is most likely to occur during periods of low humidity. If
the relative humidity is below 50%, static charges can accumulate easily.
Anytime the charge reaches about 10,000V, it is likely to discharge to grounded
metal parts.

d. 110V AC at 5 amps is much more dangerous than 25,000V DC at 5
microamperes according to the current-delivering capabilities (5 amps versus 5
microamperes) they create.

c. The ampere-hour rating of the UPS describes how long it can
supply power to a given size electrical load after a failure has
occurred.

c. Extremely high voltage levels (in excess of 25,000V) may be
present inside the CRT housing, even up to a year after electrical power has
been removed from the unit.

d. Remove all power cords associated with the computer, and its
peripherals, from the power outlet during thunder or lightning storms.

b. Computer devices should be stored or transported in their
original boxes using their original packing foam and protective storage bag
because the contours in the packing foam of these devices are not compatible
from model to model, or device to device. If the original boxes and packing
materials are not available, make sure to use sturdy cartons and cushion the
equipment well on all sides before shipping.

a, b, c. When a disruption occurs, the UPS notifies the host
computer so that its operating system can conduct an orderly shutdown of the
system without losing data. The management software can also be configured to
notify the system users to save and shut down, as well as to email or page an
administrator to alert him to the failure.

b. While touching only the insulated handle of the screwdriver,
slide the blade of the screwdriver under the rubber cup of the anode and make
contact with its metal connection. This should bleed off the high voltage charge
to ground.

Objective 3.3

c. Check your local waste management agency before disposing of
them. Some landfills will not accept chemical solvents and cans. In this case,
these items must be disposed of in a Subtitle-D dump site.

c. Free liquids are those substances that can pass through a
standard paint filter. If the liquid passes through the filter, it is free
liquid and cannot be disposed of in the landfill.

b. All hazardous materials are required to have Material Safety
Data Sheets (MSDSs) that accompany them when they change hands. They are also
required to be on hand in areas where hazardous materials are stored and
commonly used.

a, c. The MSDS contains information about what the material is,
its hazardous ingredients, its physical properties, fire and explosion data,
reactive data, spill or leak procedures, and any special protection or
precaution information.

b. Toner cartridges can be refilled and recycled. They can be very
messy to refill and often do not function as well as new cartridges do. In many
cases, the manufacturer of the product will have a policy of accepting spent
cartridges.

c. Local regulations concerning acceptable disposal methods for
computer-related components should always be checked before disposing of any
electronic equipment, such as a CRT.

a. The desired method of battery disposal is recycling. It should
not be too difficult to find a drop site that will handle recycling batteries
and other hazardous materials.

c. If the battery is expected to be stored for more than 30 days
(as you would expect the replacement for a new computer to be) then you should
fully discharge the battery and store it at normal room temperature.

c. The best place to store computer equipment is in its original
shipping box, surrounded by an antistatic bag wrapped in protective foam. The
only correct version of this scenario in this question is the antistatic bag.
Without this item, the other options are potentially harmful for digital
equipment.

b. Grounding is an important aspect of limiting electromagnetic
interference (not to be confused with destructive ESD). Proper grounding routes
induced EMI signals away from logic circuitry and toward ground potential where
it is absorbed.